Reusable fabric masks should be cleaned and/or disinfected before each use to reduce risks associated with COVID-19 AND other potentially infectious microorganisms (e.g. bacteria, viruses, and fungi). Although the general principles of mask cleaning and disinfection are the same for most fabric masks, details will vary depending on specific mask designs, features, and materials. These details should be provided by mask makers, but for those creating their own masks or acquiring masks from nontraditional sources this may not be the case. As always, please check with relevant regulatory officials and manufacturer’s instructions! In this post, we provide an overview of fabric mask cleaning and disinfection methods such as washing, boiling, and steaming, with special attention to methods appropriate for spunbond nonwoven polypropylene (NWPP) mask materials:
- Overview: A Practical Guide to Cleaning and Disinfection
- Definitions: Mask Cleaning and Disinfection
- Mask Cleaning and Washing Advice
- Mask Disinfection Advice
Deeper Dive for Mask Makers: As part of the FDA’s latest guidance for mask makers, everyone making reusable masks for COVID-19 needs to include a label with “recommended cleaning and/or disinfection materials and processes”(see the FDA EUA April 24, 2020, and MakerMask post about labeling). It doesn’t matter if it is hand-sewn, machine-sewn, cotton, spunbond nonwoven polypropylene (NWPP), or an old sock, if it is a face mask designed to contain coughs, sneezes, and/or respiratory droplets (i.e., for source control), this guidance applies and instructions for mask cleaning and disinfection are required.
- [Update 12/1/2020] The WHO updated their guidance on fabric masks with more specific information about washing masks. For details see: WHO Fabric Mask Guidance – December Updates
- [Update 6/7/2020] The WHO released guidance (June 5, 2020) on fabric masks including general information about boiling and steaming fabric masks containing combinations of cotton and NWPP. Stay tuned for guidance specific updates!
Overview: A Practical Guide to Cleaning and Disinfection
Reusable fabric face masks offer many practical benefits, but it is critical to approach reuse carefully. Starting with the basics – face masks are personal: they should be worn by one user and should not be shared. Since they are designed as a barrier to droplets that may be infectious, they should be assumed dirty after every use and should be disinfected appropriately. As with any barrier, they are less effective if damaged, so masks should be inspected for defects prior to each use and discarded if defects are detected or if concerns arise.
It should go without saying, but face masks should also be kept clean — free from food residues, dirt, contamination, and other soiling. They should be washed or laundered between uses if they become sticky, visibly soiled, and/or difficult to breathe through. If heavily soiled, face masks should be discarded.
The table below provides a framework for thinking about mask cleaning and disinfection along a risk continuum. Cleaning alone carries the highest risk, disposal after a single use carries the lowest risk, and various disinfecting strategies lie in between.
|Reuse Strategies for Community Masks
|Highest Risk Tolerance||Cleaning Alone||Washing
||Convenience and Familiarity||High degree of variability; detergent residue may cause skin irritation; fragrances and harsh chemicals may pose inhalation risks.|
|Disinfecting (with or without cleaning)||7 Days in a Paper Bag||~ 99.9% effective
Minimal effort. Does not require water. Can be used for N95s and other meltblown materials that cannot be washed or boiled.
|Requires more masks. Requires well controlled environment. Less effective than boiling.|
|Boil (MakerMask Preferred)
||~ 99.9999% effective
Commonly accessible, high degree of consistency; familiarity
|Requires attention during the 10-minute boiling time period|
|Home ‘Autoclave’ (Steam Sterilize with Pressure Cooker or Instapot)
||~ 100% effective (theoretically can sterilize)
Reduces physical agitation of materials and may extend longevity of masks
|Experimental use. Requires specialized equipment. Closer to melting point of materials. No formal evaluation for this use; unknown hazards may exist.|
|Autoclave (moist heat)
||~ 100% effective (theoretically can sterilize)
Reduces physical agitation of materials and may extend longevity of masks. Familiar to health care facilities.
|Requires specialized equipment. Not accessible to home users. Closer to melting point of materials.|
|No Risk Tolerance||DISCARD||Single use||Reduces risk of cross-contamination. Leaves high risk infection control to professional facilities.||Environmental impact. Limitations of source materials. Requires more masks|
Figure 1. NOTE: Although these mask cleaning and disinfection recommendations are thoroughly researched and have been tested in homes and facilities around the country, they have not been evaluated by the standardized processes for approval or validation through the FDA. See Disclaimer at end of document.
Inspect Masks Prior to Each Use
It is important to note that mask materials are likely to degrade over time and with repeated washing/disinfection cycles regardless of the mask materials used. For most reusable fabric masks the exact number of cycles before mask performance degrades is still unknown. However, the WHO suggests reusable masks should be able to withstand at least 5 cleaning/disinfection cycles. Prior to each use inspect masks carefully for defects and/or damage.
For fabrics like NWPP, water-resistance is expected to diminish after repeated cleaning and/or disinfection cycles. To check the water-resistance of mask materials like spunbond nonwoven polypropylene (NWPP), a ‘flick’ test can be performed by flicking water at the surface of the mask. If the water gets absorbed by the material, it is no longer water-resistant and may be less effective as a barrier to droplets. To maximize the water resistance of mask fabrics the following steps can be taken:
- Rinse fabrics thoroughly after washing as soaps and detergents are typically surfactants that reduce the water repellent properties of mask fabrics.
- Avoid fabric softeners, dryer sheets, or other conditions that lubricate fabrics and leave residues that may reduce water resistance.
- Reduce excess agitation while washing (e.g., wash on gentle cycles or place masks in lingerie bags while washing) and do NOT ring dry. Gentle handling while washing will increase the longevity of masks.
For more advice of cleaning masks see the section on Cleaning below. For more information on water-resistant mask materials see: The Big 4: Criteria for Community Mask Materials
Definitions: Mask Cleaning and Disinfection
In the context of infection control, cleaning and disinfection are different processes with different goals. For this discussion, we define cleaning and disinfecting based on the definitions used by the FDA (e.g., for medical washers y medical devices) as summarized below:
- Cleaning refers to the physical removal of organic material or soil from objects, usually done by using water with or without detergents, manually or mechanically (AAMI, 1995). In general, the goal of cleaning is to remove microorganisms and not to kill them (Garner, 1985). In the context of reusable face masks, cleaning can be accomplished by rinsing with copious amounts of water, handwashing with detergent, or machine washing in accordance with the CDC’s recommendations for face masks, “A washing machine should suffice in properly washing a face covering.“
- Disinfecting refers to the destruction of microorganisms by physical processes like heat, or by chemical means. The goal of disinfection is to kill and/or inactivate most microorganisms, but it may not kill everything (AAMI, 1995). The degree to which disinfection is successful is measured in terms of the logarithmic reduction in active pathogens (Log10 reductions), typically disinfection (i.e. pathogen inactivation) is considered successful if there is a 6 Log10 reduction in pathogens, or 99.9999% reduction, which means that only one pathogen out of every million is left.
Figure 2. Disinfectant Effectiveness on a scale of one to six where one is a 90% reduction and six is a 99.9999% reduction (image from: ‘Log Reductions – A Beginner’s Guide)
Deeper Dive: Recommendations for the degree of cleaning and disinfection required before reusing items like face masks are typically determined by which of the three Spaulding Categories it falls into based on intended use and the degree of risk to infection: critical, semi-critical, an noncritical. For noncritical devices like masks used for source control, masks may be reused after thorough cleaning and/or disinfection (FDA EUA April 24, 2014). Face masks, cloth face coverings, and fabric masks intended for use as source control are considered non-critical devices because they “are instruments and other devices whose surfaces contact only intact skin and do not penetrate it” and the “FDA recommends thorough cleaning, then intermediate or low level disinfection for non-critical devices depending on the nature and extent of contamination.” However, in home settings the CDC suggests, that noncritical items can be cleaned with a detergent and “in general, sterilization of critical items is not practical in homes but theoretically could be accomplished by … boiling.”
Mask Cleaning and Washing Advice
According to FDA reprocessing information and CDC guidance for cloth face masks, washing alone may be sufficient for fabric masks used as source control by a single individual to contain their own respiratory secretions if the mask has not been exposed to anyone else’s bodily fluids or secretions (i.e., if cross-contamination is unlikely).
Cleaning can be accomplished handwashing with detergent, or machine washing in accordance with the CDC’s recommendations for face masks, “A washing machine should suffice in properly washing a face covering.” An additional rinse cycle when cleaning a mask is recommended for all washing methods to remove any residual cleaning agents.
- Detergents: detergent residue may cause skin irritation. Consider using fragrance-free, no residue detergents for masks. For more information refer to EPA Safer Choice detergents, or see recommendations from the National Eczema Association. Occasional washing with a low concentration of distilled white vinegar (e.g., ½ cup for machine washing) may help reduce build-up of detergent residues. Detergents are surfactants, and any detergent residue may reduce the water resistance of mask fabrics. Avoid detergents with conditions that may leave residue on masks.
- Bleach: CUIDADO, in general, bleach is NOT recommended for washing face masks as residual odors and chlorine off-gassing have been reported and could cause serious irritation or harm to the wearer. Additional information about bleach is summarized in the references section at the end.
- Fabric Softener: fabric softener is NOT recommended when washing masks because it leaves a residue on mask fibers that may reduce water resistance and other technical properties of mask fabrics.
For nonwoven polypropylene (NWPP) MakerMask designs, we recommend the following washing procedures:
- Note: If handling dirty laundry from a sick individual, gloves should be worn, shaking of dirty laundry should be minimized to reduce dispersal risk, and items should be laundered using the warmest appropriate water setting for the items and dried completely.
- See JAMA for more information
Mask Disinfection Advice
Disinfection after each use is a best practice for all reusable masks, regardless of style or material. Although disinfection is commonly associated with the use of chemical treatments, it can also be achieved with heat (e.g., boiling or autoclaving), which is the preferred method for masks. Harsh chemicals (e.g., bleach) are not recommended as residuals of the chemicals can be trapped in the mask and may cause unintended inhalation risks or irritation.
The goal of disinfection is to kill anything that might be growing on, or inside the mask, with the goal of inactivating 6 Log10, or 99.9999% of pathogenic microorganisms. Although 6 Log10 disinfection cannot be guaranteed, it is the goal of the disinfection processes recommended by MakerMask.
For spunbond nonwoven polypropylene MakerMask designs, we recommend the following disinfection procedures:
Deeper Dive: One of the advantages of using 100% spunbond NWPP, such as that used in high-quality reusable grocery bags/conference bags, is that it is primarily homopolymer isotactic polypropylene, which has a melting point between 160 and
166 °C (320 to 331 °F) and is safe to boil (100 °C / 212 °F at sea level) or steam/autoclave at 121 °C / 250 °F. Industry guidance for decorating NWPP tote bags without melting suggests a maximum temperature of 275 °F. For more information see: https://makermask.org/the-big-four-criteria-for-community-mask-materials/
|Boil||100 °C||212 °F|
|Iron on Low (i.e., for pressing nylon, polypropylene and spandex)||≤ 110 °C||230 °F|
|Autoclave (moist heat; 121 °C)||121 °C||250 °F|
|Autoclave (moist heat; 132 °C)||132 °C||270 °F|
|Max. Heat Pressing Temp for NWPP Bags||135 °C||275 °F|
|Iron on Medium (i.e., for pressing polyester, silk, and wool)||≤ 150°C||≤ 302 °F|
|NWPP tote bag melting point||160°C||331 °F|
|Iron on High (i.e., for pressing cotton and linen)||200°C||392 °F|
Figure 3. Temperatures of common processes in relation to the melting point of isotactic nonwoven polypropylene, such as that found in reusable NWPP bags.
The Science of Disinfecting by Boiling
The science of disinfection by boiling is most simply understood in the context of boiling drinking water. Boiling is recommended by both the CDC and the WHO for disinfecting water because boiling inactivates bacteria, protozoa, and viruses in liquids (CDC Water Disinfection; WHO Guidelines for Drinking Water Quality).
For water, the WHO reports that bringing to a rolling boil, where large bubbles rise quickly to the surface of the liquid, for one minute and allowing to cool is a successful method for disinfection of water by typical users (6 Log10 reduction) as well as the most successful users (9+ Log10 reduction), see table below.
Figure 4. Effectiveness of methods for disinfecting water, adapted from WHO Guidelines for Drinking Water Quality (2017). Method used: “Bring water to a rolling boil and allow to cool.” Note: the cooling time is important as disinfection continues as long as the temperature of the water remains above 70°C (158°C).
|Treatment Process||Pathogen Group||Typical User
Log10 Reduction Value
Log10 Reduction Value
≥6 Log10 Reduction Value
|Thermal Disinfection (e.g. boiling)||Bacteria||6||9+||PASS|
|Solar disinfection (solar UV radiation + thermal effects)||Bacteria||3||5+||FAIL|
|UV light technologies using lamps||Bacteria||3||5+||FAIL|
Although short periods of boiling followed by long periods of cooling are effective for disinfection of water, disinfection can be also achieved through longer boiling times with shorter cooling periods.
Deeper Dive: Boiling and SARS-CoV. In general, studies have shown that boiling and other methods of thermal disinfection are effective for inactivating the SARS-CoV-1 viruses (Rabenau et al 2005, Lee at al 2005, Kariwa et al 2004, Geller et al 2012, as well as studies by the WHO). For SARS-CoV-1, the virus responsible for SARS, boiling for 10 minutes at 100 °C led to inactivation of the virus (Lee et al, 2005; Rabenau et al, 2005). The mechanism of inactivation was protein aggregation, which frequently results in loss of protein function. After boiling, SARS-CoV-1 was no longer detectible in western blot protein analyses.
For SARS-CoV-2, the virus responsible for COVID-19, more recent data demonstrated that heating fluid samples at 92°C (198°F) for 15 minutes was able to totally inactivate the virus in respiratory samples (Pastorino et al, 2020). Heating viral samples to boiling temperatures of 100°C (212°F) reduces the overall time required for the same level of inactivation.
- For an even deeper dive into the temperature dependent inactivation of SARS-CoV-1, SARS-CoV-2, and MERS-CoV, check out the data and modeling efforts by Yan et al, 2020!
The Science of Disinfecting by Steaming
For those with access to autoclaves, MakerMask recommends autoclaving with moist heat at 121C as an alternative to boiling.
According to the CDC, “moist heat in the form of saturated steam under pressure is the most widely used and the most dependable” method for disinfecting/sterilizing things. In health care settings, autoclaving is the most common method used for steam sterilization/disinfection and the temperature, time, and pressure are all carefully controlled. These parameters may vary depending on the mask materials used and degree of disinfection required. For nonwoven polypropylene (NWPP) MakerMask designs, moist heat at 121°C is recommended, as higher temperatures may be detrimental to the NWPP. In general, the guidance for steam sterilization from the WHO is to autoclave 15 minutes at 121-124 °C (200 kPa).” In the context of NWPP masks, ECRI suggests humid heat with autoclaves or pressure cookers “requires 10 minutes at 121°C at a minimum to be effective,” for steam sterilization.
As of April 2020, the CDC suggested that based on the limited research available, moist heat (steam treatment) is one of the most promising potential methods for decontaminating nonwoven polypropylene-based masks and respirators. After thorough evaluation of the literature, and feedback from users in both home and health care settings, MakerMask recommends autoclaving at 121°C (250°F), 15 psi (1 bar) pressure for 10 minutes for disinfection/sterilization of NWPP masks.
For those interested in home autoclaving options, electronic pressure cookers (e.g. Instapot) claim to be able to provide ‘scientific-grade sterilization’ at home. These claims are supported by Swenson et al, 2018: “the pressure cookers tested are a viable alternative for steam sterilizing laboratory items when an autoclave is unavailable. In this work, only 15 mins of time in the pressure cookers was necessary to inactivate the microbes in growth media such that no growth was observed.” Although data suggests that electronic pressure cookers can be used for disinfection, the safety and efficacy of their use for NWPP masks is still considered experimental. Preliminary feedback from users exploring pressure-cooker based disinfection procedures is positive, with the most commonly cited procedure adapted from Instructables: How to Sterilize Autoclavable Materials at Home Using a Pressure Cooker.
- Nota: Use electronic pressure cookers in accordance with manufacturer’s instructions, read the manual. The ‘high’ setting on electronic pressure cookers typically uses a pressure of 2–11.6 psi (0.7 bar – 0.8 bar) and a temperature of 239°F-244°F (115°C – 118°C). Maximum temperatures and pressures may vary. Use at your own risk.
PRECAUCIÓN: While methods are circulating for steam sterilization of masks in home microwaves, metallic nose wires present a significant fire hazard due to electrical arcing. Masks with metallic components should never be placed in a microwave.
Other Disinfection Methods
Other disinfection methods may be used in special circumstances in healthcare settings. However, these are not recommended for home use due to differences in mask materials, available equipment, the complexity of execution and/or potential for harm if not done correctly.
Inactivation by Inaction
Based on data from SARS-CoV-2 survival rates on various surfaces (van Doremalen et al., 2020; Chin et al., 2020), New York City has proposed that healthcare workers can store used N95 respirators in brown paper bags for 7 days in warm, dry environments to inactivate the virus. This method requires carefully controlled environments, and according to the limited data available is likely less effective (a 3+ log 10 reduction instead a 6+ log 10 reduction) than boiling (Chin et al, 2020). Although we recommend proper storage of masks between uses, we do not recommend inaction as a primary method of disinfection.
Deeper Dive: It is important to note that inactivation by inaction is used as a crisis alternate strategy with N95s and respirators constructed from meltblown polypropylene and/or other materials that are not suitable for washing and heat-based disinfection methods. The CDC recommends that N95s be re-used no more than 5 times, and that respirators should be left in paper bags for at least five days between uses based on the work by van Doremalen et al., 2020. MakerMask is more conservative in their advice, suggesting at least 7 days inactivation for masks based on addition information about virus survival on masks from Chin et al, 2020. For more information about potential re-use of N95s in healthcare settings, refer to the CDC’s guidance at: Implementing Filtering Facepiece Respirator (FFR) Reuse, Including Reuse after Decontamination, When There Are Known Shortages of N95 Respirators.
CAUTION: Storing masks in plastic bags instead of paper can lead to retention of residual moisture, longer virus lifetimes, and growth of mold and other harmful contaminants.
Hydrogen Peroxide and UV-C
Other possible sterilization methods being considered for use in healthcare settings include vaporized hydrogen peroxide gas plasma (FDA EUA) and UV-C irradiation (FDA risk note for use with CPAP machines). The latest data and suggested protocols for use with N95 masks are collected at https://www.n95decon.org/example-processes. It is important to note that ultraviolet irradiation methods are “unlikely to kill all the viruses and bacteria” in face masks with multiple layers, pleats, and/or seams. MakerMask does not recommend hydrogen peroxide plasma or UV-C methods for home use or by untrained individuals.
In summary, reusable masks should be cleaned by hand or laundered when soiled and disinfected following each use. For disinfection, MakerMask recommends boiling for 10 minutes, or autoclaving (moist heat) at 121°C (250°F), 15 psi (1 bar) pressure for 15 minutes. For those considering “inactivation by inaction” by storing masks in a brown paper bags, timelines should not be shorter than seven days.
Still have questions about mask cleaning and disinfection procedures? Join the dialogue at www.facebook.com/themakermask o www.twitter.com/themakermask.
NOTE: Although these cleaning and disinfection recommendations are thoroughly researched and have been tested in homes and facilities around the country, they have not been evaluated by the standardized processes for approval or validation through the FDA. The safety and effectiveness of the recommended procedures has not been proven and cannot be assumed. For more information about FDA required validation and reprocessing requirements see: Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labeling.
REFERENCES / DEEPER DIVES
Click on the sections below for additional details.
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